Fidelity Download - information downloaded into wrong account [Edited]

The easiest/best way to fix the issue most likely is to restore a backup file dated from before when this issue occurred (i.e., before the new brokerage account was first downloaded).

When new accounts are added for downloading Quicken will prompt you to decide what to do with the downloaded data. When you get the prompt, make sure that you carefully review each account downloaded to make sure they are properly Linked to the correct accounts or the previously linked accounts get a Do Not Add message.

The issue you describe is usually the result of not correctly Linking the downloads to the correct account(s) that were already in Quicken which then caused Quicken to think a previously linked account is actually a new account. So, now you have downloads from the new account going into the wrong account. Usually the easiest/best solution is to restore a backup file and start the process to add the new brokerage account all over, again.